1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for converting input data streams having a first sample rate to output data streams having a second data rate.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in low performance applications. These applications were complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
There are a number of problems with existing digital PWM modulation schemes. One of the problems is that audio system implementations are requiring increasing numbers of channels, and increasing flexibility in routing signals through the different channels. For example, it may be desired to design a home audio system that provides audio to all of the rooms in the house. This system may need to be able to provide music to all of the rooms or selected ones of the rooms. The system may also need to be able to provide different audio signals to different rooms. For instance, audio from a home theater system may be provided to the speakers in a home theater room, while background music may be provided to all of the other rooms. It may also be desirable for the system to be able to mix audio signals that are provided to the different rooms. For instance, an intercom signal may be mixed with the background music or other audio signals. Similarly, a business application may require the ability to provide audio to many different speakers in a building. It may be desirable to have the capability of routing various different audio signals to the different speakers so that announcements can be directed to specific areas, so that music can be provided in different areas, and so on.
These and other such applications generally require more channels than are provided in a conventional system. Existing digital PWM amplification systems typically have only as many channels as can be implemented on a single chip (e.g., two or four channels). While it is possible to provide additional channels on a single chip, this typically is not a practical solution for several reasons. For example, there simply may not be enough space on the chip to implement the additional channels. It may also be possible that there are not enough resources (e.g., processor cycles) to process all of the channels on the same chip. Further, the complexity of the design may increase dramatically with the additional channels (which would also dramatically increase the cost). Still further, even if a few additional channels could be accommodated, such a solution would not address the next generation of system requirements in which still more channels would likely be required. Still further, there are difficulties that are associated with the interaction of multiple chips, such as the synchronization of the chips. It would be necessary to synchronize the chips in order to provide coherent control of all of the channels in the system and to allow switching and mixing of the audio signals among the different channels, as desired for the home and business applications described above.